The present invention relates generally to methods and apparatus for treating a diseased human heart, and in particular to a method and apparatus for treating a patient having a severely diseased left ventricle.
The human heart has four main chambers, the right and left ventricles and the right and left atria. From the right ventricle, blood is pumped through the pulmonary artery into the lungs, where the blood is oxygenated from the alveoli. The blood then returns from the lungs through the pulmonary veins into the left atrium. After passing through the mitral valve, the blood is then pumped out of the left ventricle and into the aorta and thence into the arteries of the body. The venous system then returns the blood to the right atrium via the inferior and superior vena cava. During diastole, the heart relaxes and blood fills the atria and ventricles. During systole, the right and left ventricles contract and drive the blood from the right ventricle into the lungs, and simultaneously from the left ventricle into the aorta and its branching arteries.
One type of heart ailment is commonly referred to in layman's terms as a "diseased left ventricle". This term is applied here to any heart disease in which the contractile properties of the left ventricle are impaired.
It is known that, even when a left ventricle of a patient is in a diseased condition, the left ventricle does not cease to function entirely; rather, the capacity of the left ventricle to deliver the proper amount of blood to the aorta is only partially reduced.
There have been recent suggestions for the insertion of pumping devices through the arterial system for relief of the diseased left ventricle, in order to provide mechanical assistance in delivering blood from the diseased left ventricle into the aorta.
In U.S. Pat. No. 4,105,016, Donovan discloses the use of a centrifugal blood pump in order to reduce the pressure in either the right or left ventricle in synchronism with the ventricular contractions of a diseased heart. The pump disclosed in the Donovan '016 patent is implanted in a parallel relationship with the ventricle to be assisted, and is run at a constant speed. When the ventricular pressure reaches a predetermined value, blood automatically begins to flow through the pump, thereby reducing the maximum allowable pressure in the ventricle being assisted.
In U.S. Pat. No. 4,688,998, Olsen et al disclose a ventricular assist pump utilizing a magnetically-suspended impeller inside a centrifugal flow tube. Other prior art centrifugal heart-assist pumps are also disclosed in the following United States patents: U.S. Pat. No. 3,647,324 to Rafferty et al.; Reissue No. 28,742 to Rafferty et al; and U.S. Pat. No. 3,608,088 to Dorman et al. Similar prior art is disclosed in an article by Tanaka et al, in an article entitled "A Compact Centrifugal Blood Pump for Extracorporeal Circulation: Design and Performance", Transactions of the ASME, Vol. 109, August 1987.
In the aforementioned patents to Rafferty et al, there is a detailed discussion of the complex makeup of blood and its constituents, and the deleterious effect on blood when it is subjected to shear action or other mechanical stresses; see Col. 2, lines 19-60 of U.S. Pat. No. 3,647,324.